Rectifier.



No. 713,555. Patuntod m. n, 1902,

n. w. aucx.

RECTIFIER.

(Apyliclflm m Apr. 1:, 10am (In Inhl.)

Withesses Inventor-- Harold W. Buck mu lmhmmmur UNITED STATES PATENTOFFICE.

HAROLD W. BUCK, OF NIAGARA FALLS, NEW YORK, ASSIGNOR TO GENERA ELECTRICCOMPANY, A CORPORATION OF NEW YORK.

RECTIFIER.

SPECIFICATION forming part of Letters Patent No. 713,555, dated November11, 1902.

Original application filed October 17, 1898. Serial No. 693,694. Dividedand this application filed April 12, 1902. Serial No,

103,099. (No model.) l

T aZZ whom it may concern.-

Be it known that I, HAROLD W. BUcK,a citizen of the United States,residing at Niagara Falls, county of Niagara, State of New York,

have invented certain new and useful Improvements in Rectifiers, (CaseNo. 2,813, division of my prior application, Serial No. 693,694, filedOctober 17, 1898,) of which the following is a specification.

ratus for rectifying alternating currents, and has for its object theattainment of such advantages as flow from a sparkless commutation ofthe alternating current.

In rectifying alternating currents a commutator of well-known form iscommonly employed, the function of which is to transpose the connectionsof the alternating supply-circuit with the work-circuit as often as thecurrent in the supply-circuit changes sign, the result of whichtransposition is that the current in the work-circuit is unidirectional,while that in the supply-circuit is alternating. This transposition orcommutation may take place in either of two ways.

The supply-circuit may either be wholly disconnected from thework-circuit and then connected thereto with the terminals reversed, orthe commutation may take place by momentarily short-circuiting. thesupplycircuit, as in the case where the commutator brush or brushesoverlap the segments connected to the supply-terminals. In the lattercase, upon breaking the short circuit by fur- 3 5 ther rotation of thecommutator, the supply-terminals are connected in the reverse sense tothe work-circuit. In either of these cases, however, if the circuit beat all reactive sparking will take place at the time 0 of commutation.In the case where the supply-circuit is first broken before reversingits connections sparking will take place even though the break be madeat the precise instant when the current passing has reached 5 its zerovalue, and this because of the fact that the impressed electromotiveforce being out of phase with the current is acting at the instant ofbreak and causes the current to jump across the intervening space assoon as the terminals are separated rather than pass the alternativepath formed by the inductive work-circuit. The action is similar in thecase where the supply-terminals are shortcircuited before beingreversed. Upon breaking this short circuit current willjump across theintervening space formed as the terminals are being separated ratherthan overcome the impedance of the reactive Work-circuit.

A rectifying-commutator of the character re- IO The present inventionrelates to an appa-' ferred to will not operate sparklessly without ooadjunctive devices, except in the case ofsmall currents flowing innon-reactive circuits. It is the object of my present invention to doaway with this objectionable sparking and to accomplish the same withouteither break- 6 5 ing the work-circuit or short-circuiting the terminalsof the supply-circuit. In carrying out this object I make use of aplurality of equal and similar sources of alternating electromotiveforce, preferably of such nature that the electromotive force of eachsource is in the same phase. One of these sources, a, is first connectedinto the work-circuit, and after operating until its electromotive forcehas passed through its predetermined range and becomes zero anothersource, b, with its terminals reversed, is then connected into thework-circuit in parallel with the first source. Upon the hypothesis thatthe work-circuit is reactive the current in the source a will not followthe impressed electromotive force, but will either lag behind or beadvanced in phase with respect to the impressed electromotive force, sothat when the impressed electromotive force becomes zero there will atthat instant be a current flowing in the source a of a value dependingupon the amount of reactance. The second source of electromotive forceI) is connected with the first in a direction such as to oppose acontinuation of the flow of current in the first coil in its originaldirection after its impressed electromotive force has changed sign. Itshould be remarked that the two sources of electromotive force, althoughin parallel 5 when considered with respect to the workcircuit, are inseries when considered with respect to each other. If the circuit of thefirst source a be interrupted within the interval occurringbetween theinstant when its rco impressed electromotive force becomes zero and whenits current becomes zero, an induced electromotive force in the samedirection as the current will be produced of a value roughlyproportional to the value of the current. Within the interval mentionedthe current of the first source a decreases to zero, while the impressedelectromotive force of the second source 1) increases from zero. A pointmay therefore be found where the induced electromotive force due todisconmeeting the source a at the value which its current then has isexactly equal and opposed to the resultant of the impressedelectromotive forces of the sources a and b-or, in other words, to theimpressed electromotive force in the local circuit. If at this instantthe terminals of the first source be disconnected, no sparking will takeplace, because of the balanced electromotive forces then exv isting.

Although I have described above a mode of action which I believe to becharacteristic of an apparatus constructed in accordance with myinvention, I do not desire to be limited thereto, since I am aware thatin the operation of all such devices many modifying actions may arise toalter or qualify their modes of action. I find in practice, however,that with an apparatus constructed according to the manner hereinafterdescribed it is possible to prevent sparking in commutating alternatingcurrent into direct current, and this I consider conclusive of theutility of my invention whatever the theory may be as to the mode ofaction of the same.

Acting on the principle outlined, my invention consists in connectingone source of electromotive force a to thework-circuit before anothersource b is disconnected therefrom and causing the disconnection to takeplace at an instant such that the electromotive force due todisconnecting the source a is app roximately equal to the impressedelectromotive force in the local circuit. This mode of action will bemore readily understood by considering the same in connection with thefollowing description of the apparatus for carrying it out.

That specific embodiment of my invention which I have found it mostadvantageous to employ I have hereinafter described in connection withthe accompanying drawings, while the various features of novelty whichconstitute my invention I have distinctly and particularly pointed outin the accompanying claims.

Figure 1 is a diagrammatic representation of the circuits of my improvedrectifying device, and Fig. 2 is a view in side elevation of theapparatus employed.

The form of the invention shown in the drawings comprises two similarsources of electromotive force adapted to be alternately connected to awork-circuit, with means for opposing one electromotive force to theelectromotive force existing between the terminals of the other sourceof electromotive force at the instant of commutation. As shown in thedrawings, the electromotive forces are derived from two independentsymmetrical transformer-secondaries 1 2, receiving their energy from asingle primary winding 3. It is obvious, however, that independenttransformers or independent generators might be used. The terminals ofthe secondary coils are led to a special commutating device 4,

which acts to alternately connect the windings to a work-circuit in sucha way that one set of terminals is not disconnected until theconnections for the other set of terminals are made.

In the diagrammatic representation in Fig. 1 the terminal 5 of onesource is permanently connected, through sliding contacts or otherwise,to one side of an ordinary rectifyingcommutator 6. The correspondingterminal 7 of the other source is connected in similar manner to oneside of a second rectifying commutator 8. The remaining terminal 9 ofthe first source is connected to the other side of therectifying-commutator 8. In like manner the remaining terminal 10 of thesecond source of electromotive force 2 is connected to the other half ofthe rectifying-commutator 6. It will thus be seen that each source ofelectromotive force has one terminal connected to one commutator and theother terminal to another commutator. The commutators revolve infixedrelation to each other, and two brushes 11 and 12 are arranged tobear thereon in such a way as to make contact with those segments of thecommutators which are in connection either with one source ofelectromotive force or the other. Thus, as shown in the drawings, thework circuit through the brushes 11 and 12 is in connection with theterminals of the transformercoil 1. The other transformer-coil 2 is atthis time on open circuit. As the commutator revolves the brushes 11 and12 pass simulta-- neously from one set of segments to the next. Thework-circuit is then in connection with the coil 2, while the coil 1 isopen-circuited. The sparking which would ordinarily occur ininterrupting an electric current is in this case prevented byproportioning the parts so that the brushes 11 and 12 bridge over thespace between adjacent segments in passing from one to the other. Bythus simultaneously bridging over adjacent segments by the brushes 11and 12 at the instant of commutation it will be seen that the terminalsof the two coils 1 and 2 will be connected, so that the impressedelectromotive forces at their terminals are in series with each other.Thus if the brush 11 bridge over the insulating-space between segmentsit will be in connection simultaneously with the terminals 5 and 10 ofthe coils 1 and 2, respectively. In like manner the brush 12 will be inconnection at the same instant with the remaining terminals 7 and 9 ofthe transformer-coils.

Terminals of opposite polarity are thus con- IIO nected together. If thework-circuit be absolutely non-reactive, the current will be in phasewith theimpressed electromotive force, and zero current and zeroelectromotive force will occur at the same instant. Sparklesscommutation may in this case be secured by transposing the terminals atthe instant when the current is zero by the use of very narrow brushes,since at this instant there is no electromotive force acting. Inpractice, however, an absolutely non-reactive circuit is seldom, ifever, met with, so that the brushes must have a certain finite width inorder that the circuit of each source may not be opened until a shorttime after the other source is connected in, for reasons fully explainedabove. The position of the brushes to accomplish this result may befound by trial and will vary, depending on the nature and amount ofreactance in circuit.

Fig. 2 shows the apparatus as arranged in practice. Therectifying-commutators in this case are driven by a synchronous motor13, which has the same number of poles as the segments on eachcommutator. The brushes 11 and 12 thus bear on correspondingsegmentsduring one half a period, the connections with the work-circuit beingreversed during the succeeding half period, and thus changing analternating into a pulsating electromotive force. In order to bring thesynchronous motor up to speed, a suitable direct-current motor 14 may beemployed in a manner well understood. For convenience the entireapparatus may be mounted on a single base, which, in addition to theparts described, carries a semicircular support 15 for the commutatingbrushes. The position of the brushes may be adjusted in any suitablemanneras, for instance, by sliding them through the holders. Each of thecollecting-brushes 11 12 preferably consists of several componentbrushes, and by staggering the latter or adjusting one in advance ofanother I am enabled to obtain the effect of a brush of variable width.This means of adjustment I consider important, since it enables theattainment of the ideal condition under which each source ofelectromotive force is connected into circuit at fixed timescorresponding to the instants the impressed electromotive forces arezero, while disconnection of the same takes place at variable intervalsthereafter, so chosen as to result in a suppression of sparklng.

In practice it is found convenient to include a self-induction orreactive device L in the work-circuit in order to smooth out therectified current and prevent too violent fluctuations thereof.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is

1. The combination of two sources of alternating electromotive forceadapted to be alternately connected to a work-circuit, and means forconnecting one source to the workcircuit before the other isdisconnected therefrom.

2. The combination of two secondary coils inductively related to eachother, and means for connecting said coils to a work-circuit atoverlapping time intervals.

3. The combination of two sources of alternating electromotive force,and means for alternately connecting the sources to a workcircuitat'overlappiug time intervals;

In witness whereof I have hereunto set my hand this 10th day of April,1902.

HAROLD W. BUCK. Witnesses:

H. B. BODINE, WM. M. BLAIR.

